This invention relates to electronically controlled embroidery machines. More particularly, it relates to such embroidery machines which are subject to power interruptions.
Embroidery machines utilize a large heavy frame with a plurality of sewing needles for simultaneously embroidering on a span of fabric. The stitch design is determined by the movement of the frame between each needle stroke. The frame is driven in the x and y direction by large motors which are connected to the control apparatus by couplings such as rack and pinion or ball screws.
For many years, embroidery machines have been controlled by mechanically read punched tape operating linkages. Those types of machines are often referred to as Schiffli machines. However, modern embroidery machines are now being controlled electronically by computers.
Examples of computer-controlled embroidery machines are disclosed in U.S. Pat. No. 4,221,176, issued to Besore et al.; U.S. Pat. No. 4,365,565, issued to Kawai et al.; U.S. Pat. No. 4,391,211, issued to Yamamoto et al.; U.S. Pat. No. 4,413,574, issued to Hirota; and U.S. Pat. No. 4,478,160, issued to Ohniwa. These computer controlled embroidery machines, many of which use stepper motors with a large number of discrete movements per revolution, are more accurate and operate at higher speeds than mechanically controlled machines.
One of the problems which occurs with all embroidery machines but is a particular problem with electronically controlled embroidery machines has been situations where power is cut off to the machine while the machine is in operation. In certain parts of the country, these power outages or reductions in voltage, which will effectively provide the same results, occur quite often; in some cases, as often as 30 to 40 times annually. Loss of power to an electronically controlled embroidery machine may result in two kinds of problems: (1) loss of pattern continuity, which is also referred to as "shifting", and (2) misalignment of the tandem motors which are often used to drive the same axis of the frame. The problem results in destroyed product and loss of production time. In a closed loop system, the problems occur because the controller or computer loses the value of the desired frame position. In an open loop system, the problem is further complicated by the fact that there is no feedback information giving the present location of the frame.
One solution is to provide a source of uninterruptable power to the control circuitry and to the stepper motors. This is very expensive and most uninterruptable power supplies are limited in the amount of time that they can maintain a load. Another solution is to apply a brake to the stepper motors at the first indication of a power loss; however, this solution would only be applicable if the frame is not in motion when the power loss occurs. If the frame is in motion, the braking action is not predictable from one time to the next and from one motor to the next.